(1) Field of the Invention
This invention relates generally to battery driven mobile devices and relates more specifically to charging these mobile electronic devices from power supplies providing only limited current as e.g. universal serial bus (USB) port.
(2) Description of the Prior Art
Battery driven portable electronic devices such as cellular telephones, personal digital assistants (PDAs), etc. are becoming very popular.
The batteries of the mobile have to be recharged periodically by an external power source, using a battery charger, usually receiving power from a standard AC electrical outlet and converting the power into a low DC voltage.
The charging of the batteries is often controlled by a battery charge controller to manage the charging of the battery. It is a challenge for the designers of battery charge controllers when they are confronted with power supplies such as e.g. universal serial bus (USB) port having a limited capacity only and if the power from such a supply is not only used for the charging of the batteries but also simultaneously for the operation of the portable device.
The majority of personal computers (PCs) and laptop computers available today are provided with one or more USB ports as standard components. Besides data communication USB ports can supply power to a connected device in a limited extent. So called high-power USB ports can supply a maximum current of at least 500 mA and low-power USB ports can supply a current of usually 100 mA. Problems arise if the portable device consumes at least temporarily most of the power delivered by an USB port, or by another source having limited current capacity, for its own operation and simultaneously the batteries need power for recharging. An over current situation of such a power supply has to be avoided in any case.
There are known patents or patent publications dealing with the charging batteries of portable devices via USB ports or the like:
U.S. Patent (U.S. Pat. No. 7,034,503 to Veselic et al.) proposes an integral power node of a computer data bus, such as a USB (universal serial bus) port for a convenient source of charging power for portable communication devices. Unfortunately, USB ports have limited power capacity, making them generally incompatible with battery charge controllers (BCCs) which are designed to receive a steady, high capacity input. The invention provides a battery charging circuit, which adjusts to the parameters of an external power supply such as a USB port by adding a regulating circuit to a standard BCC design. This regulating circuit maximizes the current drawn by the BCC, while keeping the voltage to the BCC above a preset minimum (the low voltage shut off level for the BCC). If the voltage to the BCC begins to drop, the regulating circuit reduces the current drawn, so the voltage rises and stays within the operating range of the BCC.
U.S. Patent (U.S. Pat. No. 6,946,817 to Fischer et al.) discloses a system for powering and charging a mobile communication device includes a processing device, a rechargeable battery, a Universal Serial Bus (USB) interface, and a charging subsystem. The rechargeable battery is configured to supply power to the processing device. The USB interface is configured to connect to a USB port via a USB cable. The charging subsystem is coupled to the USB interface, and is configured to charge the rechargeable battery using power received from the USB interface.
U.S. Patent application publication (US 2006/0244422 to DiGiovanna et al.) discloses methods and apparatus for charging a power source comprising determining a type of power supply used by a base, communicating a charge rate to a power source charging module and providing power to the power source at a charge rate. In one embodiment, a scanner can recharge from a cradle that receives power from either a dedicated external power source or through USB by adjusting its charge rate based on a communication from the base.
Furthermore U.S. Patent (U.S. Pat. No. 6,507,172 to Sherman) discloses an universal serial bus powered battery charger primarily intended for use in battery powered hand-held and other portable devices to charge the battery or batteries within the battery powered device when the same is connected to a host device, powered hub or a bus powered hub through a universal serial bus (USB) port. The battery charger includes one or more current limits to conform to the universal serial bus current supply limit set in the USB specification. Any of the universal serial bus voltage and current limits may be used to charge batteries in the battery-powered device, such as single cell lithium-ion batteries.